Underground mining for ore or coal is a highly mechanized industry involving specialized equipment to cut through rock and coal deposits to yield a harvest of ore or coal. This use of vehicles to haul the mined material has evolved to where large heavy loads of material are moved on vehicles that must travel within the cut seams hauling material out. Many of these seams are limited in height to less than 2 meters (6 feet), typically 5 feet (60 inches) or less and can run several miles in length. Mining operations make money by quickly moving tonnage of material. The more material that can be moved the more profitable the operation can be.
To haul material from a mine, vehicles as described in U.S. Pat. No. 4,890,684 are used. These vehicles are wide and low permitting them to travel within the seams. FIGS. 4A and 4B show a representative view of an exemplary articulated vehicle. As can be readily seen the tires have a diameter almost equal to the vehicle height. The carrying load capacity combined with the size of the tires dictates the amount of ore that can be carried in the bucket or trailer. The ore is typically filled to a point just clearing the ceiling of the cut seam. To carry more ore one can add more axles and add tires as is commonly seen in large commercial dump trucks.
Historically in above ground vehicles like commercial trucks, dual wheeled axles were used to increase loads. In off-road mining the tires increased in overall diameter. For the very large carrying capacity these tires are in excess of 120 inches (10 feet) in diameter. The use of dual or multiple tires on the axles of underground vehicles has not been an accepted practice for a variety of reasons. Similarly the use of large diameter tires has not been accepted because as the tire's sidewalls are increased, the entire vehicle is elevated due to the taller, larger outside diameters, these larger OD tires when used in the seam reduce the amount of ore that can be piled on the vehicle.
Ideally very small wheels would be used to haul ore. In early mining steel rails would be laid on the mine floor to enable buckets to be moved on small steel wheels. While this yielded big carrying capacity it increased cost and labor. In today's modern mines the equipment can cut seams so fast that the use of such rails is cost prohibitive. Accordingly, underground mining relies heavily on the tire preferably foam filled or solid filled or pneumatic as the most efficient structure to carry the heavy loads.
In order to increase the durability of such tires a massively thick tread and sidewall is employed. These tires operate at relatively low speeds and thus thick rugged cut resistant tires are permissible without a major concern over heat build up caused by hysteresis.
The overall load carrying capacity is limited by the overall strength of the carcass. In a radial ply tire the carcass has generally one or more radial steel cord reinforced rubber coated plies anchored or wrapped around a pair of bead structures and has a belt structure including typically at least 2 preferably more steel cord reinforced belt layers. Bias tires have many carcass plies/layers oriented at opposing angles of 35° to 65° relative to the equatorial center plane of the tire generally and a breaker structure of several layers of inclined cord reinforced layers.
The present invention provides a solution to the problem of increasing the overall load carrying capacity of underground mine tires without requiring an increase in the outer diameter size of the tire.
The present invention is adapted to be used with currently available mining equipment without requiring any modifications to the vehicle.
The present invention permits a more efficient use of the tire and improves the overall durability and serviceability of the tire.